How can you tell if a head can't be decked anymore

[krummel21]

I was driving home from florida and about halfway back I blew my headgasket. So I can't do the work myself. They said that the valves are sticking down from the head as of right now. I had a cosmetic headgasket on before but I think I might have to just use the oem. Is there anway to tell how much more they can deck before trashing the head? I really need to get home as cheap as possible then fix it if I need to later.

 

[donniekak]

If the valves are protruding past the surface of the head it probably has already been decked to much. I always get the head surfaced after i do any valve work with the valves installed.

 

[krummel21]

Is this true even with aftermarket cams?

 

[BogusSVO]

I am working on a write up about head tech

According to the factory mits manual, only .008 can be removed total combined from the head and block.

BUT according to AERA, Automotive Engine Rebuilder Assoc. .015 can be milled from the head.

If you have +1mm valves, they will protrude below the HG surface.

New head thickness is 5.201 with a min thickness of 5.185 (AERA Specs)

if you have to go past this spec, get a thicker HG, Cometic sells them in diffrent thickness
or use the HG with a "head saver shim" SBI Part Number230-2001

Also if you use a MLS HG DO NOT LET THEM BELT SAND/SURFACE your head.


If you want to get your ride home, and do not want the shop that you are at to work on your car, rent a U-HAUL truck and trailer and load up and get home.
I have done this a few times when the trans went out on my car, and I did not have trust in the shop to do the repair work I was towed to.

the surface finish must be "smooth as glass"

http://www.dsmtuners.com/forums/new...face-4g63t-cylinder-head-mls-head-gasket.html

 

[TunaTalon]

The 4G63 is an interference engine. By definition the valves extend down past the plane of the head. When all is well the pistons are not there at the time else they "interfere" with the valves.

If the machine shop doesn't know about interference engines have the car hauled away.

 

[BogusSVO]

Tuna, I think the machine shop is saying the valves protrude below the gasket surface with the cams out.

If thats the case the intake vales need to be removed, the head surfaced, then the valves re-installed

But the shop will ###### want to sell you a full valve job.
if the head is in decent shape, tell them just to pull the valves, keep them in order, surface the head, then put the valves back in the same holes they cam out of.

 

[Littlebeeper]

there is also a iron or steel "plug" in the heads surface. after too much machining it will hit this. i'm not sure if its an indicator but i have never had a head surfaced to the point that it hits that.

 

[TunaTalon]

Tuna, I think the machine shop is saying the valves protrude below the gasket surface with the cams out.

That makes sense. The OP didn’t specify if the cams were still in.

The image of the head in my head (huh?) was just removed from the block.

You mean to say that the images in my head are not always right?

 

[BogusSVO]

there is also a iron or steel "plug" in the heads surface. after too much machining it will hit this. i'm not sure if its an indicator but i have never had a head surfaced to the point that it hits that.

I have milled the 4g head to the point that I was getting into the intake valve seat inserts.
But I have not hit some iron/steel plg in the castings.

 

[donniekak]

The 4G63 is an interference engine. By definition the valves extend down past the plane of the head. When all is well the pistons are not there at the time else they “interfere” with the valves.

If the machine shop doesn’t know about interference engines have the car hauled away.

That isn't what an interference engine means. What the term interference engine means is that at full valve lift the valves will interfere with the piston at tdc. I have been in plenty of 4g63's to know that on a stock head the valves are below the surface of the head when fully closed. bogussvo is totally correct when he says the 1mm oversized valves protrude past the deck surface. With oversized valves, a head that has been milled past the limit, or large cams, an old gasket should be torqued down and rotate the engine with the timing set with putty on the pistons to measure the valve to piston clearance.

 

[Littlebeeper]

I have milled the 4g head to the point that I was getting into the intake valve seat inserts.
But I have not hit some iron/steel plg in the castings.

on my old laser i did get that far into the head as well. one more time at the machine shop though and i would have hit that piecei'm talking about. i won't machine a head if i ever reach it. again i'm not sure if thats what its there for, but to hit it the head would have to be machined quite a bit so i would just skip to another head.